Failure to send and receive unicode (utf-16) SMS with ModemManager

Describe your issue

ModemManager currently fails to send and receive SMS with unicode characters (including emojis, may relate to #817 (closed)). This is address upstream as: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/274

What's the expected behaviour?

SMS with unicode works

What's the current behaviour?

On sending:

error: couldn't send the SMS: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Message.InvalidPduParameter: Failed to convert message text to UTF-16: Failed to convert 'ça vas' to UTF-16BE//TRANSLIT character setConversion from character set “UTF-8” to “UTF-16BE//TRANSLIT” is not supported'

On receiving, the text field is "--", and an error shows in the modemmanager log:

<warn>  [1604350804.061879] [modem0] couldn't convert SMS part contents from UTF-16BE to UTF-8: not decoding any text

How to reproduce your issue?

Send a text message through mmcli, for instance using sxmo.

What device are you using?

pinephone

On what postmarketOS version did you encounter the issue?

• edge (master branch)
• stable (v20.05 branch)

On what environment did you encounter the issue?

Phone environments

• Phosh
• Plasma Mobile
• Sxmo

Other

• No environment
• GNOME
• KDE Plasma
• Kodi
• MATE
• Shelli
• Sway
• Weston
• Xfce4
• fbkeyboard
• i3wm

How did you get postmarketOS image?

• from https://images.postmarketos.org
• I built it using pmbootstrap
• It was preinstalled on my device

What's the build date of the image? (in yyyy-mm-dd format)

Additional information

I think this is mostly an upstream issue, but according to the upstream developer it may in part be caused by the way alpine/pmos packages gettext? A patch is available for sending SMS and the upstream maintainer says: "I'll try to find a solution in MM, but I guess you can patch it in postmarketos for now". So my main question is if that would be an acceptable solution for the time being. (it only fixes sending though, receiving is still unsolved).

I'm also wondering to what extent other environments are impacted by this issue (if they rely on modemmanager they should be).

Upstream issue at ModemManager: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/274 Issue at SXMO: https://todo.sr.ht/~mil/sxmo-tickets/92 (send) and https://todo.sr.ht/~mil/sxmo-tickets/112 (receive)